Power transmission belts comprising an elastomeric body are well known in the art reinforced with one or more helical winds of a cord. Such tension member is usually a fiber glass strand treated to adhere to the elastomer. Some belts also include lateral members to provide a lateral stiffness to the belt while permitting longitudinal flexibility thereof when used especially in variable pulley drives in which the belt performs it power transmission function by engaging the pulley flanges with its edges. In the absence of the stiffeners, belts sag, become arched and distorted. This is undesirable and is to be avoided. Examples of belts with lateral stiffening means are described in U.S. patents to Ungar and Redmond, U.S. Pat. Nos., 2,189,049 and 3,772,929, respectively.